In recent years, from the viewpoint of reduction of load applied on air conditioning equipment as part of energy conservation measures, demands are increasing for near-infrared shielding films configured to be pasted on window glasses of buildings and vehicles so as to shield transmission of heat rays of sunlight.
As methods of forming a near-infrared shielding film, dry film-formation methods such as vapor deposition and sputtering are mainly proposed in which a lamination unit, is formed by alternately laminating a high refractive index layer and a low refractive index layer. However, the dry film-formation methods have problems such as need to use a large-sized vacuum apparatus for film-formation, high production cost, difficulty in formation of a film with large area, and restriction on applicable substrates limited to heat-resistant materials.
Recently, studies on methods of forming near-infrared shielding films by wet film-formation methods are actively conducted, instead of the dry film-formation methods having the above-described problems.
As a technique of wet coating methods, for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-266577 discloses a method of alternately laminating using a slurry containing particles of spherical rutile-type titanium oxide dispersed in methanol and a methanol silica sol. Moreover, for example, JP-A No. 2004-123766 discloses a method of forming a transparent laminate by coating a composition for forming a high refractive index coating film which consists of rutile-type titanium oxide, a heterocycle-based nitrogen compound (for example, pyridine), an ultraviolet curable binder, and an organic solvent on a substrate according to a wet coating method using a bar coater. Further, for example, JP-A No. Hei8-110401 discloses a method of forming a transparent laminate including using a coating liquid for a high refractive index layer in which a thermosetting silicone resin or an ultraviolet curable acryl resin containing a metal oxide or microparticles of a metal compound is dispersed in an organic solvent and coating the coating liquid on a substrate according to a wet coating method using a bar coater.